CN111564151B - Narrow-band active noise reduction optimization system for engine order noise in vehicle - Google Patents
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Abstract
The invention discloses a narrow-band active noise reduction optimization system for the order noise of an engine in a vehicle, which is used for smoothing an obtained rotating speed signal through an exponential smoothing formula aiming at the condition that the rotating speed of the engine fluctuates in the actual running process of the vehicle, constructing a more stable internal reference signal by using the smoothed rotating speed signal, obtaining an output signal of the narrow-band active noise reduction system according to the internal reference signal, and then updating the weight coefficient of a filter so as to continuously update the output signal. The system can solve the problem that the noise reduction performance of the system is reduced due to the fact that the internal reference signal presents obvious unsteady state characteristics caused by the fluctuation of the rotating speed of the engine in the actual situation, and has the potential of popularization and application in the field of active noise reduction in the vehicle.
Description
Technical Field
The invention relates to the technical field of active noise control in a vehicle, in particular to a narrow-band active noise reduction optimization system for the order noise of an engine in the vehicle.
Background
Conventionally, passive control of noise is mainly to reduce noise by three methods, i.e. controlling a noise source, cutting off a propagation path, and protecting a receiver, but these methods only can effectively reduce noise of medium and high frequency noise with short wavelength in a vehicle, and for low frequency noise with long wavelength, a thicker and heavier material, i.e. higher cost, is required to obtain a good noise reduction effect. The Active Noise Control (ANC) technique is a method for achieving the purpose of Noise reduction by reasonably arranging a microphone and a secondary sound source in a scene by using the principle of sound wave interference, can effectively suppress the Noise level of a target object under the condition of basically not increasing the weight of the target object, further improves the sound quality of the whole environment, and is an efficient and cost-effective Noise Control method.
Currently, research on an ANC system in a vehicle mainly focuses on two technologies, namely Engine Order Noise Cancellation (EOC) and Road Noise active control (RNC). The engine order noise is usually selectively controlled by a narrow-band active noise reduction (NANC) system based on a Filter-x Least Mean square (FxLMS) algorithm, a rotation speed sensor is used for obtaining a rotation speed signal, and then an internal reference signal is constructed for the narrow-band active noise reduction system according to the relationship between the frequency and the rotation speed of the order noise. However, in practical situations, the operating state of the engine is not absolutely steady, and even if the vehicle runs under a relatively steady constant speed condition, the rotating speed of the engine still fluctuates within a certain range, which will cause the constructed internal reference signal to have a significant unsteady characteristic, so that the convergence performance and the noise reduction effect of the algorithm are reduced. The principle of Exponential Smoothing (ES) is that the Exponential Smoothing value of any phase is the weighted average of the actual observed value of the phase and the Exponential Smoothing value of the previous phase. If the method can be applied to a narrow-band active noise reduction system for reducing the order noise of the engine to carry out smoothing treatment on the rotating speed signal of the engine, the method is beneficial to constructing a more stable internal reference signal, and further the performance of the system is improved and the practical application is promoted.
Disclosure of Invention
The invention aims to design and develop a narrow-band active noise reduction optimization system of the order noise of an engine in a vehicle, and aims to smooth an obtained rotating speed signal by an exponential smoothing formula aiming at the condition that the rotating speed of the engine fluctuates, construct a more stable internal reference signal by using the smoothed rotating speed signal, obtain an output signal of the narrow-band active noise reduction system according to the internal reference signal, and update a weight coefficient of a filter to update the output signal, so that the convergence performance and the noise reduction performance of a narrow-band active noise reduction algorithm are improved.
The technical scheme provided by the invention is as follows:
a narrow-band active noise reduction optimization system for the order noise of an engine in a vehicle comprises the following steps:
step one, obtaining an engine rotating speed signal;
step two, converting the engine rotating speed signal into a smooth rotating speed signal:
R(t)＝λ·R(t-1)+(1-λ)·r(t)；
wherein, r (t) is a smooth rotation speed signal, t is a time index, t is 1, 2, 3 … n, λ is a smooth index, λ has a value range of [0.9, 1 ], and r (t) is a rotation speed signal;
thirdly, obtaining the frequency of the engine order noise, the first internal reference signal and the second internal reference signal according to the smooth rotating speed signal, thereby obtaining a loudspeaker output signal of the narrow-band active noise reduction optimization system:
in the formula, y N (t) is the output signal at time t, i is the target order number, and i is 1, 2, 3 … q, q is the total number of angular frequencies of the target narrow-band component,
the first weight coefficients of the filter at the t-th time,
is the second weight coefficient, x, of the filter at the t-th moment ai (t) is the first internal reference signal, x bi And (t) is a second internal reference signal.
Preferably, the frequency of the engine order noise satisfies:
ω i ＝2πR(t)η i /60；
in the formula, ω i For the angular frequency, eta, corresponding to the ith target order component in the system reference noise signal i The harmonic number corresponding to the ith order component.
Preferably, the first internal reference signal satisfies:
x ai (t)＝cos(ω i t)；
in the formula, x ai (t) is the first internal reference signal, ω i And t is an angular frequency corresponding to the ith target order component in the system reference noise signal, is a time index, and is 1, 2 and 3 … n.
Preferably, the second internal reference signal satisfies:
x bi (t)＝sin(ω i t)；
in the formula, x bi (t) is the second internal reference signal.
Preferably, the first weight coefficient of the filter can be adaptively updated as:
in the formula,
the first weight coefficients of the filter at the t-th time,
is the first weight coefficient, mu, of the filter at the t +1 th moment N The step size is updated for the weights of the filter of the narrowband active noise reduction algorithm,
a filtered signal obtained by filtering the estimated secondary path for the first internal reference signal, e N (t) is residual noise.
Preferably, the second weight coefficient of the filter can be adaptively updated as:
in the formula,
the second weight coefficient of the filter at the t-th time,
the second weight coefficient of the filter at the time t +1,
estimated for the second internal reference signalThe resulting filtered signal is filtered.
Preferably, the first internal reference signal is filtered by the estimated secondary path to obtain a filtered signal satisfying:
in the formula,
an estimated impulse response of the secondary path transfer function.
In the formula,
an estimated impulse response of the secondary path transfer function.
Preferably, the residual noise satisfies:
e N (t)＝d N (t)-y′ N (t)；
in the formula, d N (t) is the primary desired signal, y' N And (t) is a secondary cancellation signal of the output signal at the t-th time point through the secondary path.
Preferably, the method further comprises the following steps:
the exponential smoothing module is used for carrying out exponential smoothing processing on the collected rotating speed signals and using the obtained result to construct a first internal reference signal and a second internal reference signal;
the two weight updating modules are used for updating the first weight coefficient and the second weight coefficient of the filter in real time;
a prediction filter module for receiving the results of the two weight updating modules and calculating output signals;
an error synthesis module for summing the inverses of the primary desired signal and the secondary cancellation signal, and the error synthesis module can transmit the result to the two weight update module.
The invention has the following beneficial effects:
compared with the traditional narrow-band active noise reduction system used in the vehicle, the narrow-band active noise reduction optimization system of the order noise of the engine in the vehicle, which is designed and developed by the invention, has the advantages that the convergence performance and the noise reduction performance of an algorithm under the condition that the rotating speed of the engine fluctuates can be obviously improved only by a smooth formula with a small calculation amount, so that the noise reduction effect in the vehicle is more excellent.
Drawings
FIG. 1 is a schematic block diagram of a narrow-band active noise reduction optimization system for engine order noise in a vehicle according to the present invention.
FIG. 2 is a time domain diagram of the noise reference signal in the vehicle collected under the constant speed condition with the vehicle speed of 30km/h in the comparison test according to the present invention.
FIG. 3 is a diagram of a synchronous rotational speed signal collected under a constant speed condition with a vehicle speed of 30km/h in a comparative test according to the present invention.
FIG. 4 is a frequency domain diagram of the noise reference signal in the vehicle collected under the constant speed condition with the vehicle speed of 30km/h in the comparison test according to the present invention.
FIG. 5 is a time domain diagram of the noise reference signal in the vehicle collected under the constant speed condition of the vehicle speed of 60km/h in the comparison test according to the present invention.
FIG. 6 is a diagram of a synchronous rotational speed signal collected under a constant speed condition with a vehicle speed of 60km/h in a comparative test according to the present invention.
FIG. 7 is a frequency domain diagram of the noise reference signal in the vehicle collected under the constant speed condition with the vehicle speed of 60km/h in the comparison test according to the present invention.
Fig. 8 is a graph of the amplitude-frequency response of the primary and secondary channels used in comparative experiments according to the present invention.
Fig. 9 is a graph of the phase-frequency response of the primary and secondary channels used in the comparative experiment described in the present invention.
FIG. 10 is a graph showing the smoothing effect of the exponential smoothing module of the optimized narrowband active noise reduction system in the comparison test on the rotation speed signal collected under the constant speed working condition of the vehicle speed of 30 km/h.
FIG. 11 is a frequency domain noise reduction effect diagram of noise reduction in a vehicle collected under a constant speed condition at a vehicle speed of 30km/h in a comparison test according to the present invention.
FIG. 12 is a diagram illustrating the smoothing effect of the exponential smoothing module of the optimized narrowband active noise reduction system in the comparative test on the rotation speed signal collected under the constant speed condition of 60km/h vehicle speed.
FIG. 13 is a frequency domain noise reduction effect diagram of noise reduction in a vehicle collected under a constant speed condition at a vehicle speed of 60km/h in a comparison test according to the present invention.
FIG. 14 is a graph of Mean Square Error (MSE) of noise reduction error signals collected under a constant speed condition of 30km/h vehicle speed in a comparison test according to the present invention.
FIG. 15 is a graph of Mean Square Error (MSE) of noise reduction error signals collected under a constant speed condition of 60km/h vehicle speed in a comparison test according to the present invention.
Detailed Description
The present invention is described in further detail below in order to enable those skilled in the art to practice the invention with reference to the description.
As shown in FIG. 1, the invention provides a narrow-band active noise reduction optimization system for the order noise of an engine in a vehicle, which comprises: the device comprises an exponential smoothing module, a two-weight updating module, a prediction filter module and an error synthesis module. The exponential smoothing module is used for carrying out exponential smoothing processing on the collected rotating speed signals, and using obtained results to construct a first internal reference signal and a second internal reference signal; the two weight updating modules adopt a self-adaptive iterative formula to update the coefficient of the prediction filter in real time, and transmit the obtained result to the prediction filter module; the prediction filter module is configured to calculate an output signal, and preferably, the prediction filter is a finite impulse response filter (FIR filter); the error synthesis module sums the opposite numbers of the primary desired signal and the secondary cancellation signal and transmits the obtained result to the two weight value updating module.
As shown in fig. 1, the basic principle of an active noise control system is superposition cancellation of sound waves, with iterative calculation of the algorithm of the active noise reduction system, emitting a train of signals through the loudspeaker that are in the same phase and opposite in phase as the target noise or the primary desired noise. Wherein the transfer function of the channel between the speaker and the target noise reduction region is a secondary path transfer function representing the influence of the channel on the amplitude and phase of the sound;
is an estimate of the secondary path transfer function, S (z) is the secondary path transfer function, and sets
The secondary path transfer function represents an effect on the acoustic signal that exists in reality, is objectively present and does not need to be acquired, and an estimate of the secondary path transfer function can be obtained by secondary path modeling recognition; d N (t) is the primary desired signal, also called primary noise, i.e. the noise of the target noise reduction zone in the vehicle, y N (t) is the output signal of the noise reduction system, y' N (t) is the secondary cancellation signal of the output signal through the secondary path, e N And (t) is a residual noise signal obtained after the primary noise and the secondary cancellation signal are superposed in the target noise reduction area, which is also called an error signal and is used for feeding back to the two weight updating modules to update the weights.
In the narrow-band active noise reduction subsystem, x ai (t) is the first internal reference signal of the subsystem, x bi (t) is the subsystem second internal reference signal,
a filtered signal resulting from filtering the estimated secondary path for the first internal reference signal,
a filtered signal obtained by filtering the estimated secondary path for the second internal reference signal.
When active noise reduction is carried out on the order noise of an engine in the vehicle, the noise reduction process is as follows:
firstly, carrying out exponential smoothing on a synchronous signal provided by a rotating speed sensor, namely the rotating speed signal to obtain a smooth rotating speed signal:
R(t)＝λ·R(t-1)+(1-λ)·r(t)；
where, r (t) is a smoothed rotation speed signal, t is a time index, and t is 1, 2, 3 … n, λ is a smoothing index, which is a constant, and λ has a value range of [0.9, 1 ], and r (t) is a rotation speed signal.
The frequency of the target narrow-band component, i.e., the frequency of the engine order noise, is thus calculated as:
ω i ＝2πR(n)i/60；
in the formula, omega i For the angular frequency, eta, corresponding to the ith target order component in the system reference noise signal i I is the target order, and i is 1, 2, 3 … q, q is the total number of angular frequencies of the target narrowband component.
The narrowband active noise reduction subsystem synthesizes a first internal reference signal and a second internal reference signal accordingly, and the results are as follows:
x ai (t)＝cos(ω i t)；
x bi (t)＝sin(ω i t)；
in the formula, x ai (t) is the first internal reference signal, x bi (t) is the second internal reference signal.
After the first internal reference signal and the second internal reference signal are respectively filtered by the estimated secondary path, filtered signals are obtained, and the results are as follows:
in the formula,
a filtered signal obtained by filtering the estimated secondary path for the first internal reference signal,
a filtered signal obtained by filtering the estimated secondary path for the second internal reference signal,
is the estimated impulse response of the secondary path transfer function, s (t) is the impulse response of the secondary path transfer function.
The prediction filter module performs convolution and summation on the obtained first weight coefficient and the second weight coefficient of the filter with the first internal reference signal and the second internal reference signal respectively to obtain a subsystem output signal, which is expressed as follows:
in the formula, y N (t) is the output signal at time t, i is the target order number, and i is 1, 2, 3 … q, q is the total number of angular frequencies of the target narrowband component,
the first weight coefficients of the filter at time t,
is the second weight coefficient, x, of the filter at time t ai (t) is the first internal reference signal, x bi (t) is the second internal reference signal.
The error synthesis module sums the opposite numbers of the primary desired signal and the secondary cancellation signal to obtain an error signal, and the result is as follows:
e N (t)＝d N (t)-y′ N (t)；
in the formula (d) N (t) is the primary desired signal, y' N (t) is the tth timeThe output signal passes through the secondary cancellation signal of the secondary path.
And substituting the error signal and the filtering signal into a self-adaptive iterative formula in the two weight updating modules to update the weights.
The self-adaptive iteration formula in the second weight value updating module is based on the steepest descent principle and is expressed as follows:
wherein,
the first weight coefficients of the prediction filter at time t,
predicting a first weight coefficient of the filter for the t +1 th moment;
the second weight coefficients of the prediction filter at time t,
for the second weight coefficient, mu, of the prediction filter at time t +1 N Updating step length for weight of filter of narrow-band active noise reduction subsystem, J a (t) is the first cost function of the adaptive iterative formula, J b (t) is a second cost function of the adaptive iterative formula,
is the gradient of the first cost function,
is the gradient of the second cost function.
And the first cost function and the second cost function satisfy:
J a (t)＝J b (t)＝E[e N 2 (t)]；
the gradient of the first cost function and the gradient of the second cost function are expressed as follows:
wherein e is N And (t) is an error signal, namely an output signal of the error synthesis submodule.
The updating results of the first weight coefficient and the second weight coefficient of the prediction filter can be obtained as follows:
the above processes are repeated continuously, and effective control of the engine order noise in the target scene can be achieved.
In order to test the noise reduction performance of the system provided by the invention on the order noise of the engine in the vehicle, the comparison test of the optimized narrowband active noise reduction system aiming at the order noise of the engine in the vehicle provided by the invention and the traditional narrowband active noise reduction system in the prior art is as follows:
as shown in fig. 2-4, the test results of the in-vehicle noise and the synchronous rotational speed signal under the constant speed condition with the vehicle speed of 30km/h are shown in fig. 5-7, and the test results of the in-vehicle noise and the synchronous rotational speed signal under the constant speed condition with the vehicle speed of 60km/h are shown in fig. 2 and 5, wherein the in-vehicle noise signals collected under the two conditions of 30km/h and 60km/h in fig. 2 and 5 are shown in fig. 3 and 6, the corresponding synchronous rotational speed signals collected under the two conditions are shown in fig. 4 and 7, and the spectrogram of the in-vehicle noise signals collected under the two conditions is shown in fig. 4 and 7.
In the experiment, p (z) is the primary path transfer function, s (z) is the secondary path transfer function, both of which are expressed by FIR filters with the order of 64, and the frequency responses of the two paths are shown in fig. 8 and 9, where fig. 8 is the amplitude-frequency response curve of the two paths, and fig. 9 is the phase-frequency response curve of the two paths.
The filters related in the two weight updating module and the prediction filter module in the system provided by the invention are all FIR filters with the order of 1. Wherein, the step length parameter in the two weight updating modules is mu under the working condition that the vehicle speed is 30km/h N ＝9.6×10 -4 Under the condition of 60km/h, the corresponding step length is mu N ＝1.6×10 -3 The target narrow-band component frequency of the system noise reduction corresponds to the first and second order of the engine order noise, i.e. eta 1 ＝1，η 2 ＝2。
As shown in fig. 10-13, it can be seen from the frequency domain that the conventional narrowband active noise reduction system is not ideal for controlling the engine order noise in the real vehicle, and the frequency band around the target narrowband component frequency even shows the phenomenon of sound pressure level increase, and the noise reduction performance is not good. In contrast, the system provided by the invention has a superior noise reduction effect on the suppression of engine order noise, and does not cause the increase of the noise sound pressure level of the nearby frequency band.
According to calculation, the traditional active narrow-band active noise reduction system can respectively realize the total noise reduction amount of 0.62dB and 0.86dB under two constant-speed working conditions of 30km/h and 60km/h, while the system provided by the invention can respectively realize the total noise reduction amount of 1.77dB and 1.40dB under the two working conditions, and has more outstanding noise reduction performance.
Furthermore, as shown in fig. 14 and fig. 15, which are mean square curves of error signals of two systems, it can be seen that the two systems perform substantially the same steady-state error in convergence performance as their noise reduction capability in frequency domain, and the system of the present invention exhibits better stability.
Compared with the traditional narrow-band active noise reduction system used in the automobile, the narrow-band active noise reduction optimization system of the order noise of the automobile engine designed and developed by the invention has the advantages that the convergence performance and the noise reduction performance of an algorithm under the condition that the rotating speed of the engine fluctuates can be obviously improved only by a smoothing formula with small calculation amount, specifically, the obtained rotating speed signal is smoothed by an exponential smoothing formula, a more stable internal reference signal is constructed by utilizing the smoothed rotating speed signal, the output signal of the narrow-band active noise reduction system is obtained according to the internal reference signal, and then the weight coefficient of a filter is updated to update the output signal, so that the noise reduction performance in the automobile is more excellent.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor for which the invention may be embodied with additional modifications as would be readily apparent to those skilled in the art, and the invention is therefore not limited to the details given herein and to the embodiments shown and described without departing from the generic concept as defined by the claims and their equivalents.
Claims (4)
1. A narrow-band active noise reduction optimization system for the order noise of an engine in a vehicle is characterized by comprising the following steps:
step one, obtaining an engine rotating speed signal;
step two, converting the engine rotating speed signal into a smooth rotating speed signal:
R(t)＝λ·R(t-1)+(1-λ)·r(t)；
wherein, r (t) is a smooth rotation speed signal, t is a time index, t is 1, 2, 3 … n, λ is a smooth index, λ has a value range of [0.9, 1 ], and r (t) is a rotation speed signal;
step three, obtaining the frequency of the engine order noise, the first internal reference signal and the second internal reference signal according to the smooth rotating speed signal:
ω i ＝2πR(t)η i /60；
x ai (t)＝cos(ω i t)；
x bi (t)＝sin(ω i t)；
in the formula, omega i For the angular frequency, eta, corresponding to the ith target order component in the system reference noise signal i Harmonic number, x, corresponding to the ith order component ai (t) is the first internal reference signal, x bi (t) is a second internal reference signal;
the loudspeaker output signal of the narrow-band active noise reduction optimization system is obtained by the following steps:
in the formula, y N (t) is the output signal at time t, i is the target order number, and i is 1, 2, 3 … q, q is the total number of angular frequencies of the target narrow-band component,
the first weight coefficients of the filter at the t-th time,
is the second weight coefficient, x, of the filter at the t-th moment ai (t) is the first internal reference signal, x bi (t) is a second internal reference signal;
wherein, the first weight coefficient of the filter can be adaptively updated as:
in the formula,
the first weight coefficients of the filter at the t-th time,
is the first weight coefficient, mu, of the filter at the t +1 th moment N Is a narrow bandThe weight update step size of the filter of the active noise reduction algorithm,
a filtered signal obtained by filtering the estimated secondary path of the first internal reference signal, e N (t) is residual noise;
the second weight coefficient of the filter can be adaptively updated as follows:
in the formula,
the second weight coefficients of the filter at the t-th time,
the second weight coefficients of the filter at the t +1 th time,
filtering the second internal reference signal by the estimated secondary path to obtain a filtered signal;
wherein, the narrowband of engine order noise in the car initiative noise reduction optimizing system includes:
an exponential smoothing module, configured to perform exponential smoothing on the collected engine speed signal, and use an obtained result to construct the first internal reference signal and the second internal reference signal;
the two weight updating modules are used for updating the first weight coefficient and the second weight coefficient of the filter in real time;
a prediction filter module for receiving the results of the two weight update modules and calculating output signals;
an error synthesis module for summing the inverses of the primary desired signal and the secondary cancellation signal, and the error synthesis module can transmit the result to the two weight update module.
2. The system for narrowband active noise reduction optimization of an in-vehicle engine order noise of claim 1, wherein the first internal reference signal is filtered by the estimated secondary path to obtain a filtered signal satisfying:
in the formula,
an estimated impulse response of the secondary path transfer function.
3. The system for narrowband active noise reduction optimization of an in-vehicle engine order noise of claim 2, wherein the second internal reference signal is filtered by the estimated secondary path to obtain a filtered signal satisfying:
in the formula,
an estimated impulse response of the secondary path transfer function.
4. The in-vehicle engine order noise narrowband active noise reduction optimization system of claim 3, wherein the residual noise satisfies:
e N (t)＝d N (t)-y′ N (t)；
in the formula (d) N (t) is the primary desired signal, y' N And (t) is a secondary cancellation signal of the output signal at the t-th time point through the secondary path.
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